In the method java.util.jar.JarVerifier#doneWithMeta there is redundant Hashtable.containsKey call.

if (sigFileSigners.containsKey(manifestName)) {
     CodeSigner[] codeSigners = sigFileSigners.remove(manifestName);
     verifiedSigners.put(manifestName, codeSigners);
 }

Hashtable doesn't allow null values. So, instead of pair 'containsKey'/'remove' calls, we can directly call 'remove' and then compare result with null.